Problem: Rewrite ${((5^{9})(4^{3}))^{-7}}$ in the form ${5^n \times 4^m}$.
Explanation: ${ ((5^{9})(4^{3}))^{-7} = (5^{(9)(-7)})(4^{(3)(-7)})} $ ${\hphantom{ ((5^{9})(4^{3}))^{-7}} = 5^{-63} \times 4^{-21}} $